Conventional automotive vehicle tail lamps, which may include a signal lamp therein, are typically mounted to a vehicle with a relatively small lens rake angle. To achieve a desired light intensity distribution, these lamps have light distributing facets or pillows on an inner reflector surface, or a combination of facets on a reflection surface of a lamp reflector and optical patterned lenses.
The design of the facets or pillows is important in producing a desired optical pattern. Prior art shows the use of many different methods to determine facet shape. For example, U.S. Pat. No. 5,204,820, Strobel, et. al. and, U.S. Pat. No. 5,065,287 Staiger et. al. disclose the use of a Bezier type formulation to design the surface shape of reflector pillows in a headlight application.
Such lamps are insufficient, however, when mounted on a sloping C-pillar in the rear of a hatch-back type vehicle due to the large lens rake angle of the lamp. This large rake angle results in asymmetry of the light spread due to the inclined pillow position and the deviation from linearity of the light spread where straight spread lines are changed to arced spreading curves. In addition, conventional lamps have a disadvantage in the sloping C-pillar environment since the light spreading surface is situated relatively deep inside the vehicle and side visibility is reduced by side reflector walls, particularly in the inboard direction.
To correct for these problems, conventional lamps have added features such as additional inner lenses and extra bulbs, which increase lamp expense and assembly time.